This invention provides a method of and apparatus for obtaining a dehydrated plant, while preserving its natural color, preserving its phytonutrients and controlling the microbial content in the resulting product.
Dehydrated plants are consumed in a variety of forms, from snacks slices to food supplements and vitamins. The main challenges with current dehydrating techniques is to obtain a dehydrated plant product with low microbial levels and natural color.
To obtain low microbial levels, plants are currently harvested and immediately (within 3 hours) dehydrated at high temperatures (greater than 300.degree. F.) for short residence times (10-15 minutes). While this lowers the bacterial count, it does not reduce the counts to desirable levels. Accordingly, the obtained plant product is currently subjected to hot room pasteurization (greater than 180.degree. F. for 72 hours). This produces a product which may meet the microbial standards, but changes the natural color of the plant to an unappealing brownish hue.
To solve the color degradation problem, Linaberry et al. (U.S. Pat. No. 3,973,047) describe a method of dehydrating vegetables by partially dehydrating with hot air to a moisture content less than about 30%, thereafter contacting the vegetables with a hot humid gaseous medium (a pasteurization step) and, finally, dehydrating with hot air so as to reduce the moisture content of the vegetable to less than about 8%. The microbial content of the product is .ltoreq.40 coliform/gram.
Cuel (U.S. Pat. No. 4,659,579) describes a dehydration process for moist vegetables, in particular alfalfa or beet pulp, which is aimed at reducing the energy required to dehydrate. The process involves first pressing the liquid from the vegetables, concentrating the volume of the liquid, and dehydrating the vegetables with vapor from the concentrating step. Neither the color nor the microbial content of the end product is disclosed.
Luh et al. (U.S. Pat. No. 3,879,568) describe a method of obtaining crisp, dehydrated banana slices, by slicing the fruit, steam blanching the fruit (such that the interior of the slices reaches about 85 to 95.degree. C.) and, finally, dehydrating the fruit. Apparently, the product is not substantially discolored. The microbial content of the product is not disclosed.
Similarly, Jackson et al., J. Food Science, 1996, 61(1):165-166 teach blanching banana chips prior to deep-frying to increase crispness. The microbial content and color of the product are not disclosed.
Aebi et al. (U.S. Pat. No. 5,368,873) describe a method of dehydrating vegetables by bathing the vegetables in a bath containing an osmotic agent and thereafter drying the vegetables.
Similarly, Aung et al. (U.S. Pat. No. 5,277,183) describe a method of dehydrating aromatic plant product by treating the fresh product with an osmotic agent and thereafter drying the plant to obtain a product which exhibits the overall color, flavor, phytonutrients, aroma and overall appearance similar to the fresh cut plant.
Unfortunately, none of the above teach or disclose dehydrated plant products with natural color, high phytonutrient content and low microbial content. Thus, a method of providing a dehydrated plant product with low microbial content and with natural color and phytonutrient content is desirable. Similarly, an efficient and effective apparatus for carrying out a method for producing such plant product is needed.